1. Field of the Invention
The present invention relates to an optical sensor, an optical sensor array, an optical sensor driving method, and an optical sensor array driving method.
2. Description of the Related Art
Photoelectric conversion elements using a semiconductor material such as silicon (Si) are applied to optical sensors.
In the operation of the photoelectric conversion elements that are used as the optical sensors, an electric field is applied to a PN junction or a MOS (Metal Oxide Semiconductor) structure to form a depletion layer, the formed depletion layer is exposed to light so that electron-hole pairs are generated, the electron-hole pairs are extracted as a signal, and the intensity of the light irradiated onto the depletion layer is detected.
Among these photoelectric conversion elements, a photodiode using a PN junction is most generally used. However, a phototransistor that amplifies a photocurrent is sometimes used to obtain higher sensitivity.
The conventional photoelectric conversion element is typically structured such that incident light passes through a semiconductor layer made of silicon and an electrode layer prior to arrival at the depletion layer. During the traveling, the light with short-wavelengths is particularly absorbed in these layers. For this reason, problems such as a decrease in sensitivity and an increase in wavelength dependence arise.
As a technology related to a Complementary Metal Oxide Semiconductor (CMOS) image sensor including a photodiode having a PN junction, a technology for improving efficiency of the CMOS image sensor using a transparent electrode (ITO: Indium Tin Oxide) is studied (for example, refer to Japanese Patent Application Laid-Open (JP-A) No. 2007-103591).
Further, In—Ga—Zn—O-based oxide materials (hereinafter, simply referred to as “IGZO”) has attracted attention as an active layer of a thin film transistor (TFT) showing higher mobility than amorphous silicon (a-Si) since a report made by a group of Professor Hideo Hosono, et. al. of Tokyo Institute of Technology (for example, refer to Science, 300 (2003) 1269 and Nature, 432 (2004) 488). Also, a visible light sensor using the IGZO has been reported (for example, JP-A No. 2006-165530).